What happens with sub tasks when checking parent tasks

I noticed today that I seem to have either misunderstood something in the handling of sub tasks when checkin of the parent task in which they live.

I tried this out like this:
* Create a task [Parent 1]
* Create another task [Sub 1]
* Make sure Sub 1 is a sub task of Parent 1
* Tick off (green check mark) Parent 1
* Look at the recently ticked off tasks

I cannot find the sub task related to the parent one. The parent task has become a regular task and the sub task has somehow vanished. I've been trying to figure out how to apply a decent filter to find it again but I haven't found anything working yet.
I was thinking that the sub tasks would still be tasks contained in the parent, only they would have been ticked off too (since the parent is ticked off, it is only reasonable to think that the sub tasks would too).
Am I going in the totally wrong direction here?

(By the way, in writing this post I found it quite amusing writing that the tasks get ticked off all the time. They're sensitive to interaction, I guess. ;))

If you read our page on subtasks ( http://www.toodledo.com/info/subtasks.php ) you'll see what the indented behavior is. When a parent task is completed, any uncompleted subtasks are deleted because they are assumed to be no longer relevant. If you want to save them, you need to move them out before you complete the parent.

Alright, I would like the sub tasks to be saved for later reference, as I use them for timers when I bill my clients.
Perhaps this could be a global setting, so people can choose whether to use it or not.
The difference between these settings would be that when I check a parent task, would be that all the sub tasks are checked, instead of getting deleted.

[Edit]
By the way, I'd like to ellaborate as to why I'd like this functionality.
I need it for archiving purposes and to get an overview of a specific task, even when it is checked.
I am studying at a college and it happens every so often that I, or someone else, would like to have the stuff, notes, estimations, comments, etc and by deleting the sub tasks I lose all that information.
Now, since I can move sub tasks out of the parent ones, I can "save" them. The thing here is, I name my tasks based on categories and what they contain, for instance:

I add comments and notes on each sub task if required and when I'm done I check them off, one by one. When I'm done with the course, I check of the parent task. Right now the sub tasks gets deleted.
If I were to move the sub tasks out of the parent to save them, I would get alot of generically named tasks that I don't know what they relate to until I open them and read their contents.
This more or less forces me to name the tasks and sub tasks as follows:

This is to relate them to each other so I don't have to understand their contents each time I want to read up on an old task.

Is there something I can do to improve my method or should I just wait and hope that some sort of archiving functionality of tasks and the sub tasks contained therein is developed and keep on doing what I do?
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